1. Field of the Invention
This invention relates to an envelope machine and more particularly to apparatus for changing the length of envelope blanks cut from a continuous roll of web material.
2. Description of the Prior Art
The throat of an envelope is formed by the closure flap fold and the edge of the bottom flap which is posiitoned in overlapping relation with the folded side flaps. The dimension of the throat, i.e., the distance between the closure fold and the edge of the bottom flap, must be a sufficient length to ensure that when the closure flap is folded, it overlaps the bottom flap so that the closure flap adhesive strip does not contact the inserted material. Accordingly, the envelope must be constructed with a throat dimension that is capable of accommodating the selected insert. Preferably, a change in the envelope throat dimension is accomplished by changing the length of the bottom flap while maintaining the closure flap and the envelope body portion fixed in length. To change the length of the bottom flap portion and thus the length of the envelope blank, it is necessary to change the linear speed of the endless web that is fed through the web cutting apparatus. The web cutting apparatus cuts the web material along a line that separates a bottom flap of one envelope blank from a closure flap of an adjacent envelope blank. To change the length of the bottom flap portion it is necessary to change the speed at which the pull rolls of the web feeding apparatus convey the continuous web from the supply roll. The side flaps of the envelope blank are formed by a rotatable cutter mechanism as disclosed in U.S. Pat. No. 3,782,233. The cutter blades of the rotatable cutter mechanism are rotated in phase with the moving web to cut notches at a preselected location on the web to form the side flaps and also define the side edges of the bottom and closure flaps. The length of the notches and accordingly the length of the bottom flap is varied by changing the phase relation between the cutter blades and the moving web.
The dimension of the throat of the envelope is determined by the length of the envelope blank and particularly by the amount the folded closure flap overlaps the bottom flap. Sufficient overlap must be provided to ensure that the strip of adhesive on the closure flap engages only the bottom flap and not the body portion between the closure flap fold and the edge of the bottom flap and a sufficient area of the bottom flap is engaged by the adhesive strip. This is to prevent the closure flap from adhering to the material inserted in the envelope. In order to effect a change in the dimension of the throat and, accordingly, the length of the bottom flap, the speed of rotation of the pull roll must be varied. The pull roll is drivingly connected through a gear train that connects the main drive shaft of the envelope machine or the drive shaft of one of the other components of the envelope machine, such as the envelope folder, to the pull rolls. A change in the speed of rotation of the pull rolls varies the amount the closure flap, when folded, overlaps the bottom flap. Preferably, a minimum overlap is provided to avoid excessive overlap and the accompanying expense of wasting paper with an excessive overlap.
The known method of changing the length of the envelope blank and accordingly the dimension of the envelope throat includes changing the size of gears of the gear train that drivingly connect the main drive shaft with the input to the pull roll shaft. The number of gears to be changed and the time required to remove and replace the gears is substantial. Replacement of the change gears provides for an incremental increase in the length of the bottom flap and consequently the amount of overlap between the closure flap and the bottom flap. The change intervals may vary, for example, from 1/4 in. to 5/16 in. intervals. Consequently, even though a change in length of 1/16 in. or 1/8 in. is only required, the gear change provides a 5/16 in. increase resulting in an excess of 3/16 in. Such an increase for each envelope blank requires a substantial increase in the amount of the web material consumed to merely provide the extra 1/16 or 1/8 in. in the length of the bottom flap. In addition, for each incremental change in the length of the envelope blank, an additional set of change gears must be maintained, necessitating an increase in inventory expense and the expense of replacement parts.
There is need in an envelope machine for apparatus operable to change the length of envelope blanks cut from a continuous web to thereby change the length of the bottom flap and the dimension of the envelope throat. The change in length should be carried out without having to perform time consuming operations of removing and replacing the change gears that transmit drive from the main drive shaft to the web feeding apparatus. Also, the change in length should provide infinite cut off length possibilities, provide for easy change-over to preprinted webs and provide paper savings by minimizing the seal flap overlap.